1. Field of the Invention
This invention relates to a battery voltage monitoring apparatus for detecting battery voltage of a power supply apparatus. The battery voltage monitoring apparatus includes a plurality of secondary batteries connected in series. Particularly, this invention relates to a battery voltage monitoring apparatus for detecting disconnection of a single line which is used for potential measurement.
2. Description of Related Art
An electric vehicle and hybrid vehicle are known as an eco-friendly one. In the electric vehicle and hybrid vehicle, a motor is used as driving force. Rechargeable secondary batteries are connected to the motor as electric power source. A direct current supplied from the secondary battery is converted into an alternating current, and the motor is driven by the alternating current. High voltage is required to drive the motor. Generally, the secondary battery is formed as an assembled battery including a plurality of battery cells connected in series.
A plurality of voltage sensors are used for detecting each battery cell voltage in the assembled battery. A moderate number of voltage sensors are assembled and modularized. When a large number of battery cells are connected in series such as the electric vehicle or the like, a large number of voltage sensors are also provided and connected in series. An apparatus monitoring assembled battery voltage like this is shown in Japanese Unexamined Patent Application Publication Nos. 2003-208927, 2003-111284, and 2005-117780.
An apparatus for monitoring potentials of the assembled batteries is described hereinafter in detail. In the apparatus, a module including a plurality of voltage sensors is configured as one semiconductor device (IC). A plurality of semiconductor devices are connected in series. Each semiconductor device (IC) has the plurality of battery sensors.
FIG. 11 shows a schematic view of the conventional voltage monitoring apparatus. As shown in FIG. 11, one IC is able to detect voltages of four battery cells. Each input terminal of IC is connected to a battery cell C101-C108 through lines for voltage measurement L101-L109. The IC 101 in FIG. 11 operates with a positive terminal (a node N101) of the battery cell C101 as a power supply potential and a negative terminal of the battery cell C104 (a positive terminal of battery cell C105, a node N102) as ground potential. An IC 102 is connected to the IC 101 in series. Hence, the IC 102 operates with a positive terminal (a node N102) of battery cell C105 as power supply potential, and a negative terminal (a node N103) of battery cell C108 as ground potential. When each IC detects that the monitored battery cell becomes excess voltage or low voltage, the IC outputs an excess voltage detect signal or low voltage detect signal.
Taking IC 102 of FIG. 11 for instance, the operation of a voltage sensor module outputting the excess voltage detect signal or low voltage detect signal is explained. FIG. 12 shows a configuration of conventional IC 102 in FIG. 11. As shown in FIG. 12, the voltage sensor module comprises a plurality of voltage sensors SEN101-SEN104 and output logic circuits LOG101 and LOG102. When each voltage sensor SEN101-SEN104 detects excess voltage or low voltage of the battery cell to be monitored, the voltage sensor outputs high level signal as the excess voltage detect signal or low voltage detect signal, for example. When any voltage sensor outputs the excess voltage detect signal or low voltage detect signal, output of OR circuit of output logical circuit LOG101 turns into high level from low level, for example. With this operation, the IC 102 outputs the excess voltage detect signal or low voltage detect signal. When any voltage sensor detects low voltage, the output logic circuit LOG101 outputs high level, for example. When any voltage sensor detects excess voltage, the output logic circuit LOG102 outputs low level, for example.
For the apparatus monitoring the assembled battery voltage with the plurality of series-connected ICs, the apparatus monitoring the assembled battery voltage can be configured as follows. When a line connecting the battery cells and the voltage monitoring apparatus is disconnected, the voltage sensor connected to the disconnected line monitors abnormal potential to detect disconnection. For example, this configuration is shown in our Japanese Unexamined Patent Application Publication No. 2006-275928. However, for example, when the line corresponding to a connect portion between ICs like L105 in FIG. 11 is disconnected, there are problems as follows.
When disconnection happens to the line L105 in FIG. 11, voltage supply from the battery cell is not supplied to a node N104 in FIGS. 11 and 12. Hence, current flowing out from VSS101 of IC101 flows into a VCC102 and V105 of IC 102. If the circuit is configured so that the uppermost voltage sensor SEN101 detects a defect of excess voltage for detecting disconnection, potential of the node N104 rises at disconnecting of the L105. The voltage sensor SEN101 detects excess voltage and logic output of output logic circuit LOG102 is inverted. At this time, in logic circuit LOG 102, leak current flows between VCC102 as voltage supply of IC102 and VSS102. When leak current flows, power supply potential VCC102 becomes fall and potential of node N104 becomes lower. When potential of node N104 becomes lower, the voltage sensor SEN101 does not detect excess voltage. Hence, output potential becomes lower. When output potential of voltage sensor SEN101 becomes lower than threshold of logic circuit LOG102, output logic circuit LOG102 outputs low level again. Hence, IC102 does not output excess voltage detect signal. As a result, disconnection cannot be detected. In some cases, after that, the operation is repeated, that excess voltage is detected because leak current is decrease. Then, there is the case in which output of the IC102 may be switched between high level and low level.
As described above, because of disconnection of lines, a detect signal of voltage sensor module is output incorrectly. Hence, there is a case, for battery voltage monitoring apparatus, output becomes unstable.